Unable to reduce start-up items

I am attempting to reduce my start-up programs by running msconfig ,finding the start list,and un-checking boxes. When I click ok, a note tells me"access denied please log-on as administrator" yet there is only one account listed which is mine as administrator. After restart,a box says it is running in configuration mode and will always do so unless I restore non-selective start menu, where I usually oblige and end up were I started. Any suggestions please? Am running windows XP pro.

After placing MSConfig in Diagnostic Mode, you can then run Msconfig Cleanup tool, to cleanup all the disabled entries

Ideally, instead of using Msconfig and Registry to remove common startups, it's always better to use the program's settings, usually selecting:Disable Startup checkbox
Or uninstall not required programs

Another program, that will not leave your computer in "Diagnostic Mode" is Startup Control Panel (very easy to use)

Try Glary Utilities. Launch it. Click the Modules| Optimize & Improve | Startup Manager. It's up to you to select which apps you want to Programs that are delayed started. As a rule your AntiVirus/AntiMalware/Firewall must start with Windows and shouldn't be delayed. You can also run 1-Click Maintenance once in a while to rid you system of junk.

If you already have CCleaner, launch it and go to Tools | Startup. Disable all those you no longer needed to start with Windows. Make sure you are logged on as an Administrator.

Many thanks everyone! Have had regicare7 installed for ages, didn't realise it had this facility, Just used it to clean up registry. It wasn't free but seems to do the job ok. Worked on start up a treat.